JP Patent Publication (Unexamined Application) No. 5-52721: “Method of separating a sample and a method of analyzing a separated sample obtained by the separating method” (Publication 1) discloses a method of preparing a sample by separating and removing a microscopic sample section of the micrometer order with a mechanical probe. In this publication, a change in probe potential caused by the contacting of a probe to the substrate is captured as a change in luminance in a scanning ion microscopy image (to be hereafter referred to as SIM image), to judge the contact of the probe to the substrate surface.
JP Patent Publication (Unexamined Application) No. 9-326425: “Defect inspecting method and apparatus” (Publication 2) discloses a sample examining method for measuring the characteristics of a sample by bringing a mechanical probe into contact with a specific position on the sample surface and applying a voltage to the sample surface with the probe. This method will be described by referring to FIG. 26. In this method, four probes 301, 302, 303 and 304 are contacted to electrodes 305, 306, 307 and 308, respectively, on the surface of a sample. The electric characteristics among the probes are measured to determine the electric characteristics of the sample. Initially, the sample surface is scanned by a primary electron beam 309. While observing the sample surface by picking up secondary electrons 311 with a secondary electron detector 310, the probes 301, 302, 303, and 304 are moved over the electrodes 305, 306, 307, and 308. Then, the probe 301 is contacted to the electrode 305 in the following manner. When the timing immediately before the probe contacts the sample is detected (“pre-contact detection”) based on the tunnel current or atomic force between the probe and sample, the movement of the probe is stopped temporarily. Thereafter, the probe is again moved closer to the electrode at a slower speed and stopped upon contact. The contact of the probe to the sample is judged by detecting a contact current with a probe current monitor, or by monitoring a change in potential of the electrode 305 with an energy filter-equipped secondary electron detector.
One of the most important things when contacting a probe to a specific region of a sample of the micrometer or sub-micrometer order is avoid damage to the probe or sample. For this reason, the contact detection techniques disclosed in Publications 1 and 2 are at least necessary. In addition, to avoid damage to both probe and sample, a means must be devised to minimize the amount of overshooting when stopping the probe. In Publication 1, it is possible to detect the timing at which the probe makes a contact, but the distance between the probe and the sample prior to contact cannot be known. For these reasons, the overall speed at which the probe approaches the sample must be reduced, which results in a longer time before contact is made. On the other hand, in Publication 2, the timing immediately before contact with the sample can be known by making the pre-contact detection. Therefore, while the speed is lowered immediately before contact, the time it takes for the probe to make contact can be reduced by setting the approach speed of the probe immediately before it makes contact at a high value.
However, the detection of tunnel current requires that the sample be electrically conductive, so that no detection can be made if the contact region is an insulator or a floating electrode. In the case of atomic force detection, the probe must be formed as a cantilever for the detection of microscopic forces, which is not easy and tends to raise costs. Furthermore, when detecting tunnel current or atomic force, the probe must be brought within nanometer-order distances of the sample before detection can be made, so a complicated and highly precise probe control apparatus capable of both coarse and fine movements is necessary. In addition, since a piezoelectric element is employed, it is difficult to maintain a single position after making contact due to creep phenomena or the like. For these reasons, a means of easily making the pre-contact detection is desired.
Further, in the above publications, while the probe's position in a plane parallel to the surface of the sample is monitored through an observed image, the distance between the probe and the sample can only be monitored in a region immediately prior to contact. To enable safe transportation of the probe, however, a technique must be devised which allows the distance between the probe and the sample to be readily determined at any desired position.
When a plurality of probes are used, they must be transported in a manner that they do not interfere with each other. However, the above-mentioned publications do not disclose any methods for transporting the probes in a plane parallel to the sample surface. Generally speaking, it is difficult to control the movement of the individual probes while monitoring their three-dimensional positional relationship. Thus, a transportation method is required by which interference among the probes can be easily removed.
Conventionally, the transportation of the probe to a position immediately above a contact target in a plane parallel to the sample surface is manually performed by monitoring an observed image. It is desired, however, to carry out this operation automatically, in order to lessen the burden on the operator. Thus, a transportation technique is required by which the coordinates of the probe tip and the contact target can be automatically detected.
Accordingly, it is a first object of the present invention to provide a probe driving method and probe apparatus by which damage to the probe and sample can be curbed by a simple probe control and by which contact can be made in a short time. A second object of the present invention is to provide a probe driving method and a probe apparatus which allows the operator to recognize the distance between the probe and the sample, allowing him to easily bring the probe into contact with the sample. A third object of the invention is to provide a probe apparatus which automatically recognizes the coordinates of the probe and sample, allowing the probe to be automatically contacted to a target position on the sample. A fourth object of the invention is to provide a sample preparation apparatus by which a removed sample can be reliably prepared without it being damaged as a result of contact with the probe. A fifth object of the invention is to provide a probe apparatus for accurately obtaining the characteristics of a sample by contacting a probe to the sample in a reliable manner.